Thanks for the info on Google Fonts.
Unfortunately the font Trajan is not an open source Google Font.
I bought it separately and have it as an .oft font file which is where my issue comes in.

I found info on the forum saying to upload it https://www.fontsquirrel.com and convert it somehow but most purchased fonts are blocked from being uploaded there. So in short I’m not really sure how to add it.

I see, I didn’t know they had paid fonts, that’s why I gave you that link. If you add the font via CSS it won’t appear in the backend of the site unfortunately, you would have to use CSS to display it. You can assign a class for the font for instance:

I was able to get the headers to use the custom font on the desktop version of the site using the free Use Any Fonts plugin.

I would love to get it to work without the need for a 3rd party plugin, so I could use the CSS Class to be able to apply the font to the Menu/Navigation. This method would also allow the custom font visible on mobile I assume?

I noticed the things that might have caused it not to work or have problems.
1.) Since you have replaced the url it’s already good but you forget to add the semi-colon at the end of this code:src: url('wp-content/uploads/font-organizer/TrajanPro3-Regular.otf') format('otf')

2.) You need to have different formats for it to work properly in different browsers, currently it’s otf as you can see in the code, this should be the complete code:

I suggest you convert the otf file you have here: https://everythingfonts.com/font-face it should give you all the files needed after conversion and it will have a css file which you can use to copy and paste it in Quick CSS and just replace the urls.

Sure, can you try to create a separate thread and reference the this thread there. Then give us temporary admin access, so we can check your site further, just post the details in private content so it will only be visible to moderators and the thread creator (which will be you when you create a new thread).